Weldon parts are used in many areas of industrial manufacture. They enable metal connections without making holes and form a link between a basic structure and a component which is to be fastened. For example, a go weld stud can serve to fasten pipe conduits, push buttons, plastic nuts or cable clips. Weld-on parts (e.g., studs) made of aluminum or aluminum alloys are known which can be welded to a basic part (e.g., a piece of sheet metal) which is also made of aluminum or aluminum alloys.
Under normal circumstances, freshly exposed aluminum in the presence of air immediately begins to oxidize. The oxide generally forms a layer over the entire surface and continues to grow thicker with the passage of time. The oxide layer is hard, adhesive, transparent, and up to several nanometers thick. In addition, in many circumstances, the thickness of the oxide layer may vary from spot to spot. The oxide layer is largely insoluble in a pH range between 4.5 and 8.5. Thus, the oxide layer provides the part with protection against corrosion. However, the oxide layer does, in some circumstances, adversely affect further processing steps to which the welded part may be subjected.
While this condition applies equally to sheet aluminum and to aluminum studs, the process of manufacturing aluminum studs by cold working the metal makes the condition even worse because, after cold working, the surface may be comprised of areas of freshly exposed aluminum interspersed with different areas having varying oxide layer thicknesses. Thus, in the finished stud, the thickness of the oxide layer is random and variable.
This condition causes problems during the welding of the studs to aluminum sheets because the energy required to release electrons from the oxide is lower than the energy to release electrons from bare aluminum. For example, in arc welding a stud, the arc may initiate at the center point of a rounded weld head but, after some initial melting, the arc might jump or “blow” to an adjacent region, such as an area having a thick oxide layer. If this adjacent region is seriously off-center, the result may be an unsatisfactory weld.
Therefore, there exists a need for aluminum studs that have a relatively consistent oxide layer which is capable of being satisfactorily welded to a surface, without the occurrence of arc jumping or blowing. There also exists a need for methods of producing such aluminum studs.